A Noise Like Thunder

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Given the initial communications void, there was no way of knowing how many casualties had occurred in Mexico's rural areas. But scattered damage was reported from the coastal states of Colima, Guerrero, Jalisco and Michoacan. These were close to the epicenter, which geologists located offshore near the border between Michoacan and Guerrero, some 200 miles southwest of Mexico City. Fortunately, the affected states are sparsely populated, and their rocky underpinnings provided some resistance to the tremors. Still, at least 150 people were reported killed in Jalisco and 30 in Michoacan, where two hotels were leveled at the resort of Playa Azul. The toll along the coast, too, seemed certain to rise.

The strength of the quake set skyscrapers to swaying as far north as Houston, 1,100 miles from the epicenter. A 2-ft. tidal wave rolled ashore on the coast of El Salvador, more than 800 miles to the southeast. Hawaii, 3,500 miles west of the quake in the Pacific, was alerted to prepare for an ocean swell known as a tsunami, but it never materialized.

The widespread scare was a chilling reminder that the world's well-defined quake-prone areas can be struck at any time, without warning, and with deadly effect. The same region in which last week's two quakes occurred had generated six temblors with a magnitude of at least 7.0 since 1911. Thus the latest shocks came as no surprise to seismologists, although the timing could not be pinpointed in advance. Californians living near the dangerous San Andreas Fault could only wonder when San Francisco or Los Angeles, long tagged as likely quake targets, might share Mexico City's fate.

In striking the Mexican capital, the killer quake could not have chosen a more vulnerable target. Mexico City is at the heart of the world's most populous metropolitan area. Some 18 million people, a fourth of the nation's inhabitants, are jammed into a mere 890 sq. mi., or roughly 1% of the predominantly rural country's land area. By one estimate, nearly a third of all families in Mexico City huddle together in a single room--and the average family has five members.

Beyond the human density, the capital has a shaky geological base that makes it especially susceptible to earthquakes. Mexico City is built on the soft, moist sediment of an ancient lake bed; when jolted, says Caltech Earthquake Expert George W. Housner, it reacts "like a bowl of jelly." The city has, in fact, been sinking into its soft base at up to 10 in. annually. The drop has been uneven, creating a tilt in some foundations, thus placing those buildings at greater peril than others when the earth begins to rumble.

The morning rush hour was well under way in Mexico City when the earth began to heave. Up to half a million residents crowded the Metro, bound for work or for classes. A few schools were already open, and the inevitable morning traffic jam was slowing movement on the streets, even on the tree-lined, eight-lane Paseo de la Reforma, the grand boulevard that extends through the center of the city.